JP3674973B2 - Organic electroluminescence device - Google Patents

Description

（Ｒ₁ 〜Ｒ₉₂は、それぞれ独立に、水素、炭素数１〜２０のアルキル基、アルコキシ基およびアルキルチオ基；炭素数６〜１８のアリール基およびアリールオキシ基；ならびに炭素数４〜１４の複素環化合物基からなる群から選ばれた基である。）
【００１５】
これらのなかでフェニレン基、置換フェニレン基、ビフェニレン基、置換ビフェニレン基、ナフタレンジイル基、置換ナフタレンジイル基、アントラセン−９，１０−ジイル基、置換アントラセン−９，１０−ジイル基、ピリジン−２，５−ジイル基、置換ピリジン−２，５−ジイル基、チエニレン基または置換チエニレン基が好ましい。
さらに好ましくは、フェニレン基、ビフェニレン基、ナフタレンジイル基、ピリジン−２，５−ジイル基、チエニレン基である。
【００１６】
一般式（１）のＲ、Ｒ’において、炭素数１〜２０のアルキル基としては、メチル基、エチル基、プロピル基、ブチル基、ペンチル基、ヘキシル基、ヘプチル基、オクチル基、デシル基、ラウリル基等が挙げられ、メチル基、エチル基、ペンチル基、ヘキシル基、ヘプチル基、オクチル基が好ましい。
Ｒ、Ｒ’において、炭素数６〜２０のアリール基としては、フェニル基、４−Ｃ₁ 〜Ｃ₁₂アルコキシフェニル基（Ｃ₁ 〜Ｃ₁₂は炭素数１〜１２であることを示す。以下も同様である。）、４−Ｃ₁ 〜Ｃ₁₂アルキルフェニル基、１−ナフチル基、２−ナフチル基などが例示される。
【００１７】
溶媒可溶性の観点からは、一般式（１）におけるＡｒは、１種以上の炭素数４〜２０のアルキル基、アルコキシ基およびアルキルチオ基、炭素数６〜１８のアリール基およびアリールオキシ基ならびに炭素数４〜１４の複素環化合物基から選ばれた置換基を有していることが好ましい。
【００１８】
これらの置換基としては以下のものが例示される。炭素数４〜２０のアルキル基としては、ブチル基、ペンチル基、ヘキシル基、ヘプチル基、オクチル基、デシル基、ラウリル基等が挙げられ、ペンチル基、ヘキシル基、ヘプチル基、オクチル基が好ましい。
炭素数４〜２０のアルコキシ基としては、ブトキシ基、ペンチルオキシ基、ヘキシルオキシ基、ヘプチルオキシ基、オクチルオキシ基、デシルオキシ基、ラウリルオキシ基等が挙げられ、ペンチルオキシ基、ヘキシルオキシ基、ヘプチルオキシ基、オクチルオキシ基が好ましい。
炭素数４〜２０のアルキルチオ基としては、ブチルチオ基、ペンチルチオ基、ヘキシルチオ基、ヘプチルチオ基、オクチルチオ基、デシルオキシ基、ラウリルチオ基等が挙げられ、ペンチルチオ基、ヘキシルチオ基、ヘプチルチオ基、オクチルチオ基が好ましい。
炭素数６〜１８のアリール基としては、フェニル基、４−Ｃ₁ 〜Ｃ₁₂アルコキシフェニル基、４−Ｃ₁ 〜Ｃ₁₂アルキルフェニル基、１−ナフチル基、２−ナフチル基等が例示される。
炭素数６〜１８のアリールオキシ基としては、フェノキシ基が例示される。複素環化合物基としては２−チエニル基、２−ピロリル基、２−フリル基、２−、３−または４−ピリジル基等が例示される。
これら置換基の数は、該高分子蛍光体の分子量と繰り返し単位の構成によっても異なるが、溶解性の高い高分子蛍光体を得る観点から、これらの置換基が分子量６００当たり１つ以上であることが好ましい。
【００１９】
なお、本発明の有機ＥＬ素子に用いる高分子蛍光体は、ランダム、ブロックまたはグラフト共重合体であってもよいし、それらの中間的な構造を有する高分子、例えばブロック性を帯びたランダム共重合体であってもよい。蛍光の量子収率の高い高分子蛍光体を得る観点からは完全なランダム共重合体よりブロック性を帯びたランダム共重合体やブロックまたはグラフト共重合体が好ましい。
また、本発明の有機ＥＬ素子は、薄膜からの発光を利用するので該高分子蛍光体は、固体状態で蛍光を有するものが用いられる。
【００２０】
該高分子蛍光体に対する良溶媒としては、クロロホルム、塩化メチレン、ジクロエタン、テトラヒドロフラン、トルエン、キシレンなどが例示される。高分子蛍光体の構造や分子量にもよるが、通常はこれらの溶媒に０．１ｗｔ％以上溶解させることができる。
【００２１】
本発明の高分子蛍光体は、数平均分子量がポリスチレン換算で１０³ 〜１０⁷ であり、その重合度は繰り返し構造やその割合によっても変わる。成膜性の点から一般には繰り返し構造の合計数で好ましくは４〜１００００、さらに好ましくは５〜３０００、特に好ましくは１０〜２０００である。
【００２２】
有機ＥＬ素子作成の際に、これらの有機溶媒可溶性の高分子蛍光体を用いることにより、溶液から成膜する場合、この溶液を塗布後乾燥により溶媒を除去するだけでよく、また後述するさらに電荷輸送材料や発光材料を混合した場合においても同様な手法が適用でき、製造上非常に有利である。
【００２３】
本発明の有機ＥＬ素子に用いる高分子蛍光体の合成法としては特に限定されないが、例えば、アリーレン基にアルデヒド基が２つ結合したジアルデヒド化合物と、アリーレン基にハロゲン化メチル基が２つ結合した化合物とトリフェニルホスフィンとから得られるジホスホニウム塩からのＷｉｔｔｉｇ反応が例示される。
また、他の合成法としては、アリーレン基にハロゲン化メチル基が２つ結合した化合物からの脱ハロゲン化水素法が例示される。
さらに、アリーレン基にハロゲン化メチル基が２つ結合した化合物のスルホニウム塩をアルカリで重合して得られる中間体から熱処理により該高分子蛍光体を得るスルホニウム塩分解法が例示される。
いずれの合成法においても、モノマーとして、アリーレン基以外の骨格を有する化合物を加え、その存在割合を変えることにより、生成する高分子蛍光体に含まれる繰り返し単位の構造を変えることができるので、一般式（１）で示される繰り返し単位が５０モル％以上となるように加減して仕込み、共重合してもよい。
これらのうち、Ｗｉｔｔｉｇ反応による方法が、反応の制御や収率の点で好ましい。
【００２４】
より具体的に、本発明の有機ＥＬ素子に用いられる高分子蛍光体の１つの例であるアリーレンビニレン系共重合体の合成法を説明する。
例えば、Ｗｉｔｔｉｇ反応により高分子蛍光体を得る場合は、まずビス（ハロゲン化メチル）化合物、より具体的には、２，５−ジオクチルオキシ−ｐ−キシリレンジブロミドをＮ，Ｎ−ジメチルホルムアミド溶媒中、トリフェニルホスフィンと反応させてホスホニウム塩を合成し、これとジアルデヒド化合物、より具体的にはテレフタルアルデヒドとを、エチルアルコール中、リチウムエトキシドを用いて縮合させる方法により、フェニレンビニレン基と２，５−ジオクチルオキシ−ｐ−フェニレンビニレン基を含む高分子蛍光体が得られる。このとき、共重合体を得るために２種類以上のジホスホニウム塩および／または２種類以上のジアルデヒド化合物を反応させてもよい。
【００２５】
これらの高分子蛍光体を有機ＥＬ素子の発光材料として用いる場合、その純度が発光特性に影響を与えるため、合成後、再沈精製、クロマトグラフによる分別等の純化処理をすることが好ましい。
【００２６】
本発明の有機ＥＬ素子において、公知の発光材料を高分子蛍光体と共に使用することができる。例えば、ナフタレン誘導体、アントラセンおよびその誘導体、ペリレンおよびその誘導体、ポリメチン系、キサンテン系、クマリン系、シアニン系などの色素類、８−ヒドロキシキノリンおよびその誘導体の金属錯体、芳香族アミン、テトラフェニルシクロペンタジエンおよびその誘導体、テトラフェニルブタジエンおよびその誘導体等を用いることができる。具体的には、例えば特開昭５７−５１７８１号、同５９−１９４３９３号公報に記載されているもの等、公知のものが使用可能である。
【００２７】
次に、本発明の有機ＥＬ素子に用いられる陰極について説明する。
本発明における陰極は、１層または２層以上の金属層からなり、発光層に隣接する金属層（以下、これを該金属層が１層の場合も２層以上の場合も発光層に隣接する金属層を第１の金属層ということがある。）がアルカリ金属である第１金属および該第１金属を安定化せしめる第２金属（以下、安定化金属ということがある。）からなる混合金属層または合金層からなる。該混合金属または合金中の該第１金属濃度は０．００５〜１０ｗｔ％であり、好ましくは１〜２ｗｔ％である。該第１の金属層の厚みは１０〜３００ｎｍである。
ここで、混合金属層とは、二種以上の金属が実質的に合金となることなしに、互いに混じり合っている金属層のことをいい、例えば通常の方法では合金とならない組合せの第１金属と第２金属とを共蒸着法によって作製された金属層などが挙げられる。
【００２８】
また、本発明の陰極は、第１の金属層に隣接して特定の金属からなる第２の金属層を積層した陰極である。また、本発明の陰極は、第１、第２の金属層を積層した陰極または第１の金属層からなる陰極に隣接してヤング率の小さい金属からなる第３の金属層を積層した陰極である。
ここで、第１金属は、アルカリ金属であればよく、具体的には、リチウム、カリウム、ルビジウム等が挙げられ、リチウム、ルビジウムが好ましく、リチウムが特に好ましい。
該第１金属の酸化等を防ぎ、第１金属を安定化せしめる第２金属としては、銀、金、銅、マグネシウム、カルシウム、ストロンチウム、亜鉛、スカンジウム、イットリウム、アルミニウム、インジウム、ビスマス、クロム、鉄およびニッケルからなる群から選ばれた金属等が例示される。これらの中で、銀、亜鉛、アルミニウム、インジウムが好ましく、アルミニウム、インジウムがさらに好ましい。
第１の金属層として、具体的にはリチウムアルミニウム合金、リチウム銀合金、リチウムインジウム合金、カリウムアルミニウム合金、カリウム銀合金、カリウムインジウム合金等が挙げられる。
第１の金属層の作成方法としては、蒸着法、スパッタリング法等が例示されるが、蒸着法が好ましい。例えば、アルカリ金属を主成分とする合金からの蒸着、アルカリ金属と他の成分との共蒸着によって作成することができる。
【００２９】
陰極の第２の金属層として用いられる金属は、金、銀、白金、アルミニウム、チタン、ニオブ、タンタル、クロム、鉄、コバルトおよびニッケル並びにそれらを主成分として含む合金からなる群から選ばれるものである。さらに、該第２の金属層は、該金属の不動態薄膜を含んでいてもよい。
該第２の金属層の作成方法としては、陰極の第１の金属層までを作成した後に、蒸着法、スパッタリング法等により金属薄膜を形成する方法、金属箔上に第１の金属層、有機層、透明電極等を順に形成する方法が例示されるが、蒸着法により金属薄膜を形成する方法が好ましい。
第２の金属層の厚さは、１ｎｍ以上１０００ｎｍ以下が好ましく、蒸着法やスパッタリング法等で作成する場合は、あまり厚くすると柔軟性が失われ、経済的でもないので、１ｎｍ以上３００ｎｍ以下が好ましく、３ｎｍ以上２００ｎｍ以下であればさらに好ましい。
【００３０】
陰極の第３の金属層は、ヤング率が小さい金属または合金からなることが好ましく、具体的にはヤング率の値としては、１ＧＰａ以上６０ＧＰａ以下が好ましく、１ＧＰａ以上４０ＧＰａ以下がさらに好ましい。第３の金属層としては、インジウム、インジウムマグネシウム合金、鉛、ビスマス、アンチモン等が挙げられる。
さらに、該第３の金属層は、アルカリ金属を含んでいてもよく、具体的にはインジウムリチウム合金等が挙げられる。
該第３の金属層の作成方法としては、第２の金属層までを作成した後に、蒸着法、スパッタリング法等により金属薄膜を形成する方法、金属箔上に陰極第２の金属層、第１の金属層、有機層、透明電極等を順に形成する方法が例示されるが、蒸着法金属薄膜を形成する方法が好ましい。
第３の金属層の厚さは、特に制限はないが、蒸着法やスパッタリング法等で作成する場合は、あまり薄くすると第１の金属層または第２の金属層と外気との遮断が十分でなくなるので、１００ｎｍ以上が好ましく、３００ｎｍ以上であればさらに好ましい。
【００３１】
本発明の有機ＥＬ素子の構造については、前記の本発明の特徴を有するほかは特に制限はなく、公知の構造が採用される。
例えば、該高分子蛍光体からなる発光層、または該高分子蛍光体と電荷輸送材料（電子輸送材料と正孔輸送材料の総称を意味する）との混合物からなる発光層の両面に一対の電極を有する構造のものが挙げられる。
また、発光層と陽極との間に正孔輸送材料を含有する正孔輸送層を設けたものが挙げられる。このとき、正孔輸送層は該発光層に隣接することが好ましい。
また、発光層と陰極との間に電子輸送材料を含有する電子輸送層を設けたものが挙げられる。このとき、電子輸送層は該発光層に隣接することが好ましい。
さらに、発光層と陽極との間に正孔輸送材料を含有する正孔輸送層を設け、かつ発光層と陰極との間に電子輸送材料を含有する電子輸送層を設けたもの等が挙げられる。
また、発光層や電荷輸送層は、それぞれ独立に１層でも複数の層を組み合わせてもよい。
さらに、発光層に例えば下記に述べる該高分子蛍光体以外の発光材料を混合使用してもよい。また、該高分子蛍光体および／または電荷輸送材料を高分子化合物に分散させた層とすることもできる。
【００３２】
本発明の高分子蛍光体とともに使用される電荷輸送材料、すなわち、電子輸送材料または正孔輸送材料としては公知のものが使用でき、特に限定されないが、正孔輸送材料としてはピラゾリン誘導体、アリールアミン誘導体、スチルベン誘導体、トリフェニルジアミン誘導体等が挙げられる。また、電子輸送材料としてはオキサジアゾール誘導体、アントラキノジメタンおよびその誘導体、ベンゾキノンおよびその誘導体、ナフトキノンおよびその誘導体、アントラキノンおよびその誘導体、テトラシアノアンスラキノジメタンおよびその誘導体、フルオレノン誘導体、ジフェニルジシアノエチレンおよびその誘導体、ジフェノキノン誘導体、８−ヒドロキシキノリンおよびその誘導体の金属錯体等が挙げられる。
【００３３】
具体的には、特開昭６３−７０２５７号、同６３−１７５８６０号公報、特開平２−１３５３５９号、同２−１３５３６１号、同２−２０９９８８号、同３−３７９９２号、同３−１５２１８４号公報に記載されているもの等が例示される。
正孔輸送材料としてはトリフェニルジアミン誘導体が好ましく、電子輸送材料としてはオキサジアゾール誘導体、ベンゾキノンおよびその誘導体、アントラキノンおよびその誘導体、８−ヒドロキシキノリンおよびその誘導体の金属錯体が好ましい。特に、正孔輸送材料としては４，４’−ビス（Ｎ（３−メチルフェニル）−Ｎ−フェニルアミノ）ビフェニルが好ましく、電子輸送材料としては２−（４−ビフェニリル）−５−（４−ｔ−ブチルフェニル）−１，３，４−オキサジアゾール、ベンゾキノン、アントラキノン、トリス（８−キノリノール）アルミニウムが好ましい。
これらのうち、電子輸送性の化合物と正孔輸送性の化合物のいずれか一方、または両方を同時に使用すればよい。これらは単独で用いてもよいし、２種類以上を混合して用いてもよい。
【００３４】
発光層と電極との間にさらに電荷輸送層を設ける場合、これらの電荷輸送材料を使用して電荷輸送層を形成すればよい。
また、電荷輸送材料を発光層に混合して使用する場合、電荷輸送材料の使用量は使用する化合物の種類等によっても異なるが、十分な成膜性と発光特性を阻害しない範囲で適宜決めればよい。通常、発光材料に対して１〜４０重量％が好ましく、さらに好ましくは２〜３０重量％である。
【００３５】
次に、本発明の発光材料を用いた有機ＥＬ素子の代表的な作製方法について述べる。透明または半透明である陽極または陰極としては、ガラス、透明プラスチック等の透明基板の上に、透明または半透明の電極を形成したものが用いられる。
陽極の材料としては、導電性の金属酸化物膜、半透明の金属薄膜等が用いられる。具体的にはインジウム・スズ・オキサイド（ＩＴＯ）、酸化スズ等からなる導電性ガラスを用いて作成された膜（ＮＥＳＡなど）、金、白金、銀、銅の薄膜等が用いられる。作製方法としては真空蒸着法、スパッタリング法、メッキ法などが用いられる。
【００３６】
この陽極上に、発光材料として上記高分子蛍光体、または該高分子蛍光体と電荷輸送材料を含む発光層を形成する。形成方法としてはこれら材料の溶融液、溶液または混合液を使用してスピンコーティング法、キャスティング法、ディッピング法、バーコート法、ロールコート法等の塗布法が例示されるが、溶液または混合液をスピンコーティング法、キャスティング法、ディッピング法、バーコート法、ロールコート法等の塗布法により成膜する方法が特に好ましい。
【００３７】
発光層の膜厚としては１ｎｍ〜１μｍが好ましく、さらに好ましくは２〜５００ｎｍである。電流密度を上げて発光効率を上げるためには５〜２００ｎｍの範囲が好ましい。
なお、発光層を塗布法により薄膜化した場合には、溶媒を除去するため、発光層形成後に、減圧下または不活性雰囲気下で、好ましくは３０〜３００℃、さらに好ましくは６０〜２００℃の温度で加熱乾燥することが望ましい。
【００３８】
該発光層の下に正孔輸送層を積層する場合には、上記の成膜方法で発光層を設ける前に、正孔輸送層を形成することが好ましい。
正孔輸送層の成膜方法としては、特に限定されないが、粉末状態からの真空蒸着法、または溶液に溶かした後のスピンコーティング法、キャスティング法、ディッピング法、バーコート法、ロールコート法等の塗布法、または高分子化合物と電荷輸送材料とを溶液状態または溶融状態で混合し分散させた後のスピンコーティング法、キャスティング法、ディッピング法、バーコート法、ロールコート法等の塗布法を用いることができる。
混合する高分子化合物としては、特に限定されないが、電荷輸送を極度に阻害しないものが好ましく、また可視光に対する吸収が強くないものが好適に用いられる。
【００３９】
例えば、ポリ（Ｎ−ビニルカルバゾール）、ポリアニリンおよびその誘導体、ポリチオフェンおよびその誘導体、ポリ（ｐ−フェニレンビニレン）およびその誘導体、ポリ（２，５−チエニレンビニレン）およびその誘導体、ポリカーボネート、ポリアクリレート、ポリメチルアクリレート、ポリメチルメタクリレート、ポリスチレン、ポリ塩化ビニル、ポリシロキサンなどが例示される。
成膜が容易に行なえるという点では、高分子化合物を用いる場合は塗布法を用いることが好ましい。
【００４０】
正孔輸送層の膜厚は、少なくともピンホールが発生しないような厚みが必要であるが、あまり厚いと、素子の抵抗が増加し、高い駆動電圧が必要となり好ましくない。したがって、電荷輸送層の膜厚は好ましくは１ｎｍ〜１μｍ、さらに好ましくは２ｎｍ〜５００ｎｍ、特に好ましくは５〜２００ｎｍである。
【００４１】
また、該発光層の上にさらに電子輸送層を積層する場合には、上記の成膜方法で発光層を設けた後にその上に電子輸送層を形成することが好ましい。
【００４２】
電子輸送層の成膜方法としては、特に限定されないが、粉末状態からの真空蒸着法、または溶液に溶かした後のスピンコーティング法、キャスティング法、ディッピング法、バーコート法、ロールコート法等の塗布法、または高分子化合物と電荷輸送材料とを溶液状態または溶融状態で混合し分散させた後のスピンコーティング法、キャスティング法、ディッピング法、バーコート法、ロールコート法等の塗布法を用いることができる。
混合する高分子化合物としては、特に限定されないが、電荷輸送を極度に阻害しないものが好ましく、また可視光に対する吸収が強くないものが好適に用いられる。
【００４３】
例えば、ポリ（Ｎ−ビニルカルバゾール）、ポリアニリンおよびその誘導体、ポリチオフェンおよびその誘導体、ポリ（ｐ−フェニレンビニレン）およびその誘導体、ポリ（２，５−チエニレンビニレン）およびその誘導体、ポリカーボネート、ポリアクリレート、ポリメチルアクリレート、ポリメチルメタクリレート、ポリスチレン、ポリ塩化ビニル、ポリシロキサン等が例示される。
成膜が容易に行なえるという点では、高分子化合物を用いる場合は塗布法を用いることが好ましい。
【００４４】
電子輸送層の膜厚は、少なくともピンホールが発生しないような厚みが必要であるが、あまり厚いと、素子の抵抗が増加し、高い駆動電圧が必要となり好ましくない。したがって、電子輸送層の膜厚は好ましくは１ｎｍ〜１μｍ、さらに好ましくは２〜５００ｎｍ、特に好ましくは５〜２００ｎｍである。
【００４５】
次いで、発光層または電子輸送層の上に先に説明した陰極を設ける。該陰極の作製方法としては、前記のとおり真空蒸着法、スパッタリング法等が用いられる。
【００４６】
【作用】
本発明の有機ＥＬ素子が優れているのは、融点や分解温度が比較的高い高分子材料を用いているので熱的に安定であり、塗布法により容易に発光層を形成できることから、非常に容易に高輝度、高発光効率の有機ＥＬ素子を作製することができるからである。さらに、アルカリ金属を０．０１ｗｔ％以上１０ｗｔ％以下含む合金からなる陰極を用いることにより、電子注入効率が高い陰極を有しているため、素子の発光効率が高く、駆動電圧が低くなる。その上、第２、第３の金属層の作用により、陰極の耐久性が高くなるので長寿命化ができ、ダークスポットの生成を抑える効果があると考えられる。
【００４７】
【実施例】
以下本発明の実施例を示すが、本発明はこれらに限定されるものではない。
ここで、数平均分子量については、クロロホルムを溶媒として、ゲルパーミエーションクロマトグラフィー（ＧＰＣ）によりポリスチレン換算の数平均分子量を求めた。
実施例１
＜高分子蛍光体１の合成＞
２，５−ジオクチルオキシ−ｐ−キシリレンジブロミドをＮ，Ｎ−ジメチルホルムアミド溶媒中、トリフェニルホスフィンと反応させてホスホニウム塩を合成した。得られたホスホニウム塩４７．８重量部、およびテレフタルアルデヒド６．７重量部を、エチルアルコールに溶解させた。５．８重量部のリチウムエトキシドを含むエチルアルコール溶液をホスホニウム塩とジアルデヒドのエチルアルコール溶液に滴下し、室温で３時間重合させた。一夜室温で放置した後、沈殿を濾別し、エチルアルコールで洗浄後、クロロホルムに溶解し、これにエタノールを加え再沈生成した。得られた沈殿物を減圧乾燥して、重合体８．０重量部を得た。これを高分子蛍光体１という。
モノマーの仕込み比から計算される高分子蛍光体１の繰り返し単位とそのモル比を下記に示す。
【化４】

該高分子蛍光体１のポリスチレン換算の数平均分子量は、１．０×１０⁴ であった。該高分子蛍光体１の構造については赤外吸収スペクトル、ＮＭＲで確認した。
【００４８】
＜素子の作成および評価＞
スパッタリングによって、４０ｎｍの厚みでＩＴＯ膜を付けたガラス基板に、ポリビニルカルバゾールの１．０ｗｔ％クロロホルム溶液を用いて、ディッピングにより５０ｎｍの厚みで成膜した。さらに、高分子蛍光体１の１．０ｗｔ％トルエン溶液を用いて、スピンコートにより５０ｎｍの厚みで成膜した。
さらに、これを減圧下１５０℃で１時間乾燥した後、電子輸送層として、トリス（８−キノリノール）アルミニウム（以下、Ａｌｑ₃ と記すことがある。）を０．１〜０．２ｎｍ／ｓの速度で３５ｎｍ蒸着した。その上に陰極の第１の金属層としてリチウム−アルミニウム合金（リチウム濃度：１ｗｔ％）を４０ｎｍ蒸着して有機ＥＬ素子を作製した。蒸着のときの真空度はすべて８×１０^-6Ｔｏｒｒ以下であった。
この素子に電圧１２．５Ｖを印加したところ、電流密度３２．１ｍＡ／ｃｍ² の電流が流れ、輝度１８９２ｃｄ／ｍ² の黄緑色のＥＬ発光が観察された。このときの発光効率は、５．９ｃｄ／Ａであった。輝度はほぼ電流密度に比例していた。また、ＥＬピーク波長は５４０ｎｍで、高分子蛍光体１の薄膜の蛍光ピーク波長とほぼ一致しており高分子蛍光体１よりのＥＬ発光が確認された。
この素子を初期輝度２００ｃｄ／ｍ² で定電流駆動したところ、ダークスポットの発生は少なく、また、輝度が半減するまでの時間は３１０時間以上であった。
【００４９】
比較例１
陰極の第１の金属層としてリチウム−アルミニウム合金の代わりに厚さ５０ｎｍのマグネシウム−銀合金（重量比Ｍｇ：Ａｇ＝９：１）を用いた以外は、実施例１と同じ方法で素子を作成した。この素子に電圧１２．５Ｖを印加したところ、電流密度４４．５ｍＡ／ｃｍ² の電流が流れ、輝度１４４５ｃｄ／ｍ² の黄緑色のＥＬ発光が観察された。このときの発光効率は、３．３ｃｄ／Ａであった。輝度はほぼ電流密度に比例していた。また、ＥＬピーク波長は５４０ｎｍで、高分子蛍光体１の薄膜の蛍光ピーク波長とほぼ一致しており高分子蛍光体１よりのＥＬ発光が確認された。
この素子を初期輝度２００ｃｄ／ｍ² で定電流駆動したところ、実施例１の素子に比べてダークスポットの発生が多く、また、約２５０時間で輝度が半減した。
【００５０】
比較例２
陰極第一層としてリチウム−アルミニウム合金の代わりに厚さ５０ｎｍのアルミニウムを用いた以外は、実施例１と同じ方法で素子を作成した。この素子に電圧１２．５Ｖを印加したところ、電流密度１．１４ｍＡ／ｃｍ² の電流が流れ、輝度２１ｃｄ／ｍ² の黄緑色のＥＬ発光が観察された。このときの発光効率は、１．８ｃｄ／Ａであった。輝度はほぼ電流密度に比例していた。また、ＥＬピーク波長は５３６ｎｍで、高分子蛍光体１の薄膜の蛍光ピーク波長とほぼ一致しており高分子蛍光体１からのＥＬ発光が確認された。
この素子を初期輝度２０ｃｄ／ｍ² で定電流駆動したところ、実施例１の素子に比べてダークスポットの発生が多く、また、約３０時間で輝度が半減した。
【００５１】
【表１】

このように、実施例１の高分子蛍光体からなる層と陰極にアルカリ金属の合金層を用いた有機ＥＬ素子は、陰極にアルカリ金属の合金層を用いない比較例１および比較例２の有機ＥＬ素子よりも、高い輝度と高い発光効率を有するなど、優れたＥＬ特性を示した。
【００５２】
実施例２
陰極の第１の金属層としてリチウム−アルミニウム合金を蒸着後、第２の金属層として金を１０ｎｍ、次いで第３の金属層としてインジウムを５００ｎｍ蒸着して陰極を作成した以外は、実施例１と同じ方法で素子を作成した。
この素子を３日間空気中で保管した後、直流１０Ｖで駆動したところ、ダークスポットのない明るい発光が得られた。
【００５３】
比較例３
比較例１、２の素子を作成した素子を３日間空気中で保管した後、直流１０Ｖで駆動したところ、実施例２の素子に比べてダークスポットの発生が多く、約８０％の領域が発光しなかった。
このように、実施例２の高分子蛍光体からなる層と陰極の第１の金属層にアルカリ金属の合金層を、第２の金属層として金を、次いで第３の金属層としてインジウムを陰極として用いた有機ＥＬ素子は、陰極にマグネシウム銀合金やアルミニウムを用いた比較例１、２の有機ＥＬ素子よりも、ダークスポットの発生を抑える等、優れたＥＬ特性を示した。
【００５４】
【発明の効果】
本発明の有機ＥＬ素子は、高輝度、高発光効率、低駆動電圧であり、作成が容易であり、さらにダークスポットがほとんど生成しないので、バックライトとしての面状光源またはフラットパネルディスプレイ等の装置として好ましく使用できる。[0001]
[Industrial application fields]
The present invention relates to an organic electroluminescence element (hereinafter sometimes referred to as an organic EL element) using a polymeric fluorescent substance for a light emitting layer and a metal for a cathode.
[0002]
[Prior art]
Inorganic electroluminescence elements using inorganic phosphors as light emitting materials (hereinafter sometimes referred to as inorganic EL elements) are used for display devices such as planar light sources and flat panel displays as backlights, for example. High voltage alternating current was required to emit light.
Recently, Tang et al. Proposed an organic EL device having a two-layer structure in which an organic fluorescent dye is used as a light-emitting layer and an organic charge transport compound used in an electrophotographic photoreceptor or the like is laminated (Japanese Patent Laid-Open No. Sho 59). -194393). Compared to inorganic EL elements, organic EL elements have the characteristics that light emission of a large number of colors can be easily obtained in addition to low voltage drive and high luminance, so there are many element structures, organic fluorescent dyes, and organic charge transport compounds. An attempt has been reported [Japanese Journal of Applied Physics (Jpn. J. Appl. Phys.), 27, L269 (1988)], [Journal of Applied Physics (J. Appl. Phys.) 65, 3610 (1989)].
[0003]
Up to now, low molecular weight organic fluorescent dyes have been generally used as the material for the light emitting layer, and as high molecular weight light emitting materials, WO90113148, JP-A-3-244630, Applied Physics. -Letters (Appl. Phys. Lett.), 58, 1982 (1991). In an example of the specification of WO90113148, a poly (p-phenylene vinylene) thin film converted into a conjugated polymer is obtained by forming a soluble precursor on an electrode and performing a heat treatment. An EL device that has been disclosed is disclosed.
Japanese Patent Application Laid-Open No. 3-244630 exemplifies a conjugated polymer having characteristics that it is soluble in a solvent and does not require heat treatment. Applied Physics Letters (Appl. Phys. Lett.), 58, 1982 (1991) also describes a polymer light-emitting material soluble in a solvent and an organic EL device produced using the same. However, the organic EL device produced using these materials does not necessarily have a sufficiently high luminous efficiency.
[0004]
A single material such as aluminum, magnesium, a magnesium indium alloy, a magnesium aluminum alloy, a magnesium silver alloy, or a co-deposited alloy material is used as a cathode metal material for an organic EL element using a low molecular organic fluorescent dye. Examples are 63-295695, JP-A 63-264692 and JP-A-2-15595. Further, calcium (WO92 / 16023 published specification) is used in an organic EL element using a polymeric fluorescent substance.
[0005]
On the other hand, the use of a metal having a small work function as the cathode is exemplified in JP-A-5-121172 and JP-A-5-198380, which show the effects of high efficiency and low driving voltage. An example in which a metal having a low Young's modulus is deposited to protect the electrode is disclosed in Japanese Patent Laid-Open No. 6-295788.
[0006]
[Problems to be solved by the invention]
However, since organic EL devices using polymers reported so far do not necessarily have high luminous efficiency, a large current has to be passed in order to emit light with high luminance. Further, there has been a demand for improvement in display quality, such as a decrease in luminance during driving in a relatively short time and a defect having a low luminance called a dark spot on the light emitting surface.
[0007]
An object of the present invention is to provide an organic electroluminescence device that uses a polymeric fluorescent substance, has high luminance, high luminous efficiency, low driving voltage, and is easy to produce, and further, an organic electroluminescence device that hardly generates dark spots. There is to do.
[0008]
[Means for Solving the Problems]
As a result of intensive investigations in view of such circumstances, the present inventors have stabilized the first metal that is an alkali metal and the first metal in an organic EL element having a light-emitting layer made of a polyarylene vinylene polymer fluorescent substance. By using a cathode made of a second metal (hereinafter sometimes referred to as a stabilizing metal), an organic EL element with high luminance and high luminous efficiency can be obtained, and a specific second metal layer, third It has been found that an organic electroluminescence device in which almost no dark spots are generated can be obtained by laminating these metal layers, and the present invention has been achieved.
[0009]
That is, the present invention is the invention described below.
[1] In an organic electroluminescent device having at least a light emitting layer between a pair of anodes and cathodes, at least one of which is transparent or translucent, the light emitting layer has fluorescence in a solid state, and has the following general formula ( 1) The number of repeating units represented by 1) is 50 mol% or more of all repeating units, and the number average molecular weight in terms of polystyrene is 10 ^Three -10 ⁷ The cathode is composed of one or more metal layers, and the thickness of the metal layer adjacent to the light emitting layer (referred to as the first metal layer) is 10 to 300 nm, The first metal layer comprises a mixed metal layer or alloy layer comprising a first metal that is an alkali metal and a second metal that stabilizes the first metal, and the concentration of the first metal in the mixed metal or alloy is 0. 0.0005 to 10 wt% of an organic electroluminescence element.
[Chemical formula 2]
-Ar-CR = CR'- (1)
(Here, Ar is an arylene group or heterocyclic compound group having 4 to 20 carbon atoms involved in the conjugated bond, R and R ′ are each independently hydrogen, an alkyl group having 1 to 20 carbon atoms. And a group selected from the group consisting of an aryl group having 6 to 20 carbon atoms, a heterocyclic compound having 4 to 20 carbon atoms, and a cyano group.)
[0010]
[2] A second metal layer made of a metal selected from the group consisting of gold, silver, platinum, aluminum, titanium, niobium, tantalum, chromium, iron, cobalt and nickel, further adjacent to the first metal layer The organic electroluminescent element according to [1], wherein the second metal layer has a thickness of 1 to 1000 nm.
[2] A second metal layer made of a metal selected from the group consisting of gold, silver, aluminum, nickel, titanium, and cobalt is laminated further adjacent to the first metal layer, The thickness of a metal layer is 1-1000 nm, The organic electroluminescent element as described in [1] characterized by the above-mentioned.
[0011]
[3] The electroluminescent device according to [1], wherein a metal layer made of a metal having a Young's modulus of 1 to 60 GPa is laminated adjacent to the first metal layer.
[4] The electroluminescent device according to [2], wherein a third metal layer made of a metal having a Young's modulus of 1 to 60 GPa is laminated adjacent to the second metal layer.
[0012]
Hereinafter, the organic EL device of the present invention will be described in detail.
The polymeric fluorescent substance used for the light emitting layer of the organic EL device of the present invention is a polymer having 50% by mole or more of the repeating units represented by the general formula (1) based on the total repeating units. Although it depends on the structure of the repeating unit, the repeating unit represented by the general formula (1) is preferably 70% or more of the entire repeating unit. The polymeric fluorescent substance includes a divalent aromatic compound group or a derivative thereof, a divalent heterocyclic compound group or a derivative thereof, or a combination thereof as a repeating unit other than the repeating unit represented by the general formula (1). The resulting group may be included.
In addition, the repeating unit represented by the general formula (1) and other repeating units may be linked by a non-conjugated unit having an ether group, an ester group, an amide group, an imide group, or the like. The non-conjugated part may be contained.
[0013]
In the polymeric fluorescent substance used in the present invention, Ar in the general formula (1) is an arylene group or heterocyclic compound group having 4 or more and 20 or less carbon atoms involved in the conjugated bond. Examples thereof include a divalent aromatic compound group or a derivative group thereof, a divalent heterocyclic compound group or a derivative group thereof, or a group obtained by combining them.
[0014]
[Chemical 3]

(R ₁ ~ R ₉₂ Are each independently a group consisting of hydrogen, an alkyl group having 1 to 20 carbon atoms, an alkoxy group and an alkylthio group; an aryl group and aryloxy group having 6 to 18 carbon atoms; and a heterocyclic compound group having 4 to 14 carbon atoms Is a group selected from )
[0015]
Among these, phenylene group, substituted phenylene group, biphenylene group, substituted biphenylene group, naphthalenediyl group, substituted naphthalenediyl group, anthracene-9,10-diyl group, substituted anthracene-9,10-diyl group, pyridine-2, A 5-diyl group, a substituted pyridine-2,5-diyl group, a thienylene group or a substituted thienylene group is preferred.
More preferred are a phenylene group, a biphenylene group, a naphthalenediyl group, a pyridine-2,5-diyl group, and a thienylene group.
[0016]
In R and R ′ of the general formula (1), examples of the alkyl group having 1 to 20 carbon atoms include methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, heptyl group, octyl group, decyl group, A lauryl group etc. are mentioned, A methyl group, an ethyl group, a pentyl group, a hexyl group, a heptyl group, and an octyl group are preferable.
In R and R ′, the aryl group having 6 to 20 carbon atoms includes a phenyl group, 4-C ₁ ~ C ₁₂ Alkoxyphenyl group (C ₁ ~ C ₁₂ Indicates that the number of carbon atoms is 1 to 12. The same applies to the following. ), 4-C ₁ ~ C ₁₂ Examples thereof include an alkylphenyl group, a 1-naphthyl group, and a 2-naphthyl group.
[0017]
From the viewpoint of solvent solubility, Ar in the general formula (1) represents one or more alkyl groups having 4 to 20 carbon atoms, alkoxy groups and alkylthio groups, aryl groups having 6 to 18 carbon atoms, aryloxy groups, and carbon numbers. It preferably has a substituent selected from 4 to 14 heterocyclic compound groups.
[0018]
Examples of these substituents are as follows. Examples of the alkyl group having 4 to 20 carbon atoms include a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a decyl group, and a lauryl group, and a pentyl group, a hexyl group, a heptyl group, and an octyl group are preferable.
Examples of the alkoxy group having 4 to 20 carbon atoms include a butoxy group, a pentyloxy group, a hexyloxy group, a heptyloxy group, an octyloxy group, a decyloxy group, a lauryloxy group, and the like, such as a pentyloxy group, a hexyloxy group, and a heptyl group. An oxy group and an octyloxy group are preferable.
Examples of the alkylthio group having 4 to 20 carbon atoms include a butylthio group, a pentylthio group, a hexylthio group, a heptylthio group, an octylthio group, a decyloxy group, and a laurylthio group, and a pentylthio group, a hexylthio group, a heptylthio group, and an octylthio group are preferable.
Examples of the aryl group having 6 to 18 carbon atoms include a phenyl group and 4-C ₁ ~ C ₁₂ Alkoxyphenyl group, 4-C ₁ ~ C ₁₂ Examples thereof include an alkylphenyl group, a 1-naphthyl group, and a 2-naphthyl group.
Examples of the aryloxy group having 6 to 18 carbon atoms include a phenoxy group. Examples of the heterocyclic compound group include a 2-thienyl group, 2-pyrrolyl group, 2-furyl group, 2-, 3- or 4-pyridyl group.
The number of these substituents varies depending on the molecular weight of the polymeric fluorescent substance and the constitution of the repeating unit, but from the viewpoint of obtaining a highly soluble polymeric fluorescent substance, these substituents are one or more per 600 molecular weight. It is preferable.
[0019]
The polymeric fluorescent substance used in the organic EL device of the present invention may be a random, block or graft copolymer, or a polymer having an intermediate structure thereof, for example, a random copolymer having a block property. It may be a polymer. From the viewpoint of obtaining a polymer fluorescent substance having a high fluorescence quantum yield, a random copolymer having a block property and a block or graft copolymer are preferable to a complete random copolymer.
In addition, since the organic EL element of the present invention utilizes light emission from a thin film, the polymer fluorescent substance having fluorescence in a solid state is used.
[0020]
Examples of the good solvent for the polymeric fluorescent substance include chloroform, methylene chloride, dichloroethane, tetrahydrofuran, toluene, xylene and the like. Although depending on the structure and molecular weight of the polymeric fluorescent substance, it can usually be dissolved in these solvents in an amount of 0.1 wt% or more.
[0021]
The polymeric fluorescent substance of the present invention has a number average molecular weight of 10 in terms of polystyrene. ^Three -10 ⁷ The degree of polymerization varies depending on the repeating structure and the ratio. In general, the total number of repeating structures is preferably 4 to 10000, more preferably 5 to 3000, and particularly preferably 10 to 2000 from the viewpoint of film formability.
[0022]
When forming a film from a solution by using these organic solvent-soluble polymeric fluorescent substances when preparing an organic EL device, it is only necessary to remove the solvent by drying after applying this solution. The same technique can be applied even when a transport material or a light emitting material is mixed, which is very advantageous in production.
[0023]
The method for synthesizing the polymeric fluorescent substance used in the organic EL device of the present invention is not particularly limited. For example, a dialdehyde compound in which two aldehyde groups are bonded to an arylene group and two halogenated methyl groups are bonded to the arylene group. A Wittig reaction from a diphosphonium salt obtained from the above compound and triphenylphosphine is exemplified.
As another synthesis method, a dehydrohalogenation method from a compound in which two halogenated methyl groups are bonded to an arylene group is exemplified.
Further, a sulfonium salt decomposition method for obtaining the polymeric fluorescent substance by heat treatment from an intermediate obtained by polymerizing a sulfonium salt of a compound having two halogenated methyl groups bonded to an arylene group with an alkali is exemplified.
In any synthesis method, a compound having a skeleton other than an arylene group is added as a monomer, and the structure of the repeating unit contained in the resulting polymeric fluorescent substance can be changed by changing the ratio of its presence. You may add and subtract so that the repeating unit shown by Formula (1) may be 50 mol% or more, and you may copolymerize.
Among these, the method by Wittig reaction is preferable in terms of reaction control and yield.
[0024]
More specifically, a method for synthesizing an arylene vinylene copolymer, which is one example of the polymeric fluorescent substance used in the organic EL device of the present invention, will be described.
For example, when obtaining a polymeric fluorescent substance by the Wittig reaction, first, a bis (methyl halide) compound, more specifically, 2,5-dioctyloxy-p-xylylene dibromide in an N, N-dimethylformamide solvent. By reacting with triphenylphosphine to synthesize a phosphonium salt and condensing it with a dialdehyde compound, more specifically terephthalaldehyde, using lithium ethoxide in ethyl alcohol, the phenylene vinylene group and 2 , 5-dioctyloxy-p-phenylene vinylene group is obtained. At this time, in order to obtain a copolymer, two or more kinds of diphosphonium salts and / or two or more kinds of dialdehyde compounds may be reacted.
[0025]
When these polymeric fluorescent substances are used as the light emitting material of the organic EL device, the purity affects the light emission characteristics. Therefore, it is preferable to carry out a purification treatment such as reprecipitation purification and fractionation by chromatography after synthesis.
[0026]
In the organic EL device of the present invention, a known luminescent material can be used together with the polymeric fluorescent substance. For example, naphthalene derivatives, anthracene and derivatives thereof, perylene and derivatives thereof, polymethine series, xanthene series, coumarin series, cyanine series pigments, 8-hydroxyquinoline and derivative metal complexes, aromatic amines, tetraphenylcyclopentadiene And its derivatives, tetraphenylbutadiene and its derivatives, and the like can be used. Specifically, known ones such as those described in JP-A-57-51781 and 59-194393 can be used.
[0027]
Next, the cathode used for the organic EL device of the present invention will be described.
The cathode in the present invention is composed of one or two or more metal layers, and is adjacent to the light emitting layer (hereinafter referred to as the light emitting layer regardless of whether the metal layer is one layer or two or more layers). The metal layer may be referred to as a first metal layer.) Is a mixed metal composed of a first metal that is an alkali metal and a second metal that stabilizes the first metal (hereinafter also referred to as a stabilizing metal). It consists of a layer or an alloy layer. The concentration of the first metal in the mixed metal or alloy is 0.005 to 10 wt%, preferably 1 to 2 wt%. The thickness of the first metal layer is 10 to 300 nm.
Here, the mixed metal layer refers to a metal layer in which two or more kinds of metals are mixed with each other without substantially forming an alloy. For example, the first metal in a combination that does not form an alloy by a normal method. And a metal layer prepared by co-evaporation with the second metal.
[0028]
The cathode of the present invention is a cathode in which a second metal layer made of a specific metal is laminated adjacent to the first metal layer. In addition, the cathode of the present invention is a cathode in which a first metal layer is laminated or a cathode in which a third metal layer made of a metal having a small Young's modulus is laminated adjacent to the cathode made of the first metal layer. is there.
Here, the 1st metal should just be an alkali metal, Specifically, lithium, potassium, rubidium etc. are mentioned, Lithium and rubidium are preferable and lithium is especially preferable.
As the second metal which prevents the oxidation of the first metal and stabilizes the first metal, silver, gold, copper, magnesium, calcium, strontium, zinc, scandium, yttrium, aluminum, indium, bismuth, chromium, iron And a metal selected from the group consisting of nickel and the like. Among these, silver, zinc, aluminum, and indium are preferable, and aluminum and indium are more preferable.
Specific examples of the first metal layer include a lithium aluminum alloy, a lithium silver alloy, a lithium indium alloy, a potassium aluminum alloy, a potassium silver alloy, and a potassium indium alloy.
Examples of the method for forming the first metal layer include a vapor deposition method and a sputtering method, but a vapor deposition method is preferable. For example, it can be prepared by vapor deposition from an alloy containing an alkali metal as a main component or by co-vapor deposition of an alkali metal and other components.
[0029]
The metal used as the second metal layer of the cathode is selected from the group consisting of gold, silver, platinum, aluminum, titanium, niobium, tantalum, chromium, iron, cobalt and nickel and alloys containing them as main components. is there. Furthermore, the second metal layer may include a passive film of the metal.
As a method for forming the second metal layer, after forming up to the first metal layer of the cathode, a method of forming a metal thin film by vapor deposition, sputtering, etc., the first metal layer on the metal foil, organic A method of forming layers, transparent electrodes and the like in order is exemplified, but a method of forming a metal thin film by vapor deposition is preferred.
The thickness of the second metal layer is preferably 1 nm or more and 1000 nm or less, and when formed by vapor deposition or sputtering, flexibility is lost if it is too thick, and it is not economical, so 1 nm or more and 300 nm or less is preferable. More preferably, it is 3 nm or more and 200 nm or less.
[0030]
The third metal layer of the cathode is preferably made of a metal or alloy having a low Young's modulus. Specifically, the value of Young's modulus is preferably 1 GPa or more and 60 GPa or less, and more preferably 1 GPa or more and 40 GPa or less. Examples of the third metal layer include indium, an indium magnesium alloy, lead, bismuth, and antimony.
Furthermore, this 3rd metal layer may contain the alkali metal, and an indium lithium alloy etc. are mentioned specifically ,.
As the method for forming the third metal layer, after forming up to the second metal layer, a method of forming a metal thin film by vapor deposition, sputtering, or the like, a cathode second metal layer on the metal foil, the first The method of forming the metal layer, the organic layer, the transparent electrode, etc. in this order is exemplified, but the method of forming the vapor deposition method metal thin film is preferred.
The thickness of the third metal layer is not particularly limited, but when it is formed by vapor deposition or sputtering, the first metal layer or the second metal layer can be sufficiently shielded from the outside air if made too thin. Therefore, it is preferably 100 nm or more, and more preferably 300 nm or more.
[0031]
There is no restriction | limiting in particular about the structure of the organic EL element of this invention except having the characteristic of the said this invention, A well-known structure is employ | adopted.
For example, a pair of electrodes on both sides of a light emitting layer made of the polymer fluorescent material or a light emitting layer made of a mixture of the polymer fluorescent material and a charge transport material (meaning a generic name of an electron transport material and a hole transport material) The thing of the structure which has is mentioned.
Moreover, what provided the positive hole transport layer containing a positive hole transport material between a light emitting layer and an anode is mentioned. At this time, the hole transport layer is preferably adjacent to the light emitting layer.
Moreover, what provided the electron carrying layer containing an electron carrying material between a light emitting layer and a cathode is mentioned. At this time, the electron transport layer is preferably adjacent to the light emitting layer.
Furthermore, a hole transport layer containing a hole transport material is provided between the light emitting layer and the anode, and an electron transport layer containing an electron transport material is provided between the light emitting layer and the cathode. .
In addition, the light emitting layer and the charge transport layer may each independently be a single layer or a combination of a plurality of layers.
Further, for example, a light emitting material other than the polymeric fluorescent substance described below may be mixed and used in the light emitting layer. Moreover, it can also be set as the layer which disperse | distributed this polymeric fluorescent substance and / or charge transport material to the high molecular compound.
[0032]
A charge transport material used with the polymeric fluorescent substance of the present invention, that is, a known material can be used as the electron transport material or the hole transport material, and is not particularly limited, but examples of the hole transport material include pyrazoline derivatives, arylamines. Derivatives, stilbene derivatives, triphenyldiamine derivatives and the like. Electron transport materials include oxadiazole derivatives, anthraquinodimethane and its derivatives, benzoquinone and its derivatives, naphthoquinone and its derivatives, anthraquinone and its derivatives, tetracyanoanthraquinodimethane and its derivatives, fluorenone derivatives, diphenyldicyano Examples include ethylene and derivatives thereof, diphenoquinone derivatives, and metal complexes of 8-hydroxyquinoline and derivatives thereof.
[0033]
Specifically, JP-A-63-70257, JP-A-63-175860, JP-A-2-135359, JP-A-2-135361, JP-A-2-209998, JP-A-3-37992, and JP-A-3-152184. The thing etc. which are described in the gazette are illustrated.
The hole transport material is preferably a triphenyldiamine derivative, and the electron transport material is preferably an oxadiazole derivative, benzoquinone and a derivative thereof, anthraquinone and a derivative thereof, or a metal complex of 8-hydroxyquinoline and a derivative thereof. In particular, 4,4′-bis (N (3-methylphenyl) -N-phenylamino) biphenyl is preferable as the hole transport material, and 2- (4-biphenylyl) -5- (4- t-Butylphenyl) -1,3,4-oxadiazole, benzoquinone, anthraquinone, and tris (8-quinolinol) aluminum are preferred.
Of these, one or both of an electron transporting compound and a hole transporting compound may be used simultaneously. These may be used singly or in combination of two or more.
[0034]
When a charge transport layer is further provided between the light-emitting layer and the electrode, the charge transport layer may be formed using these charge transport materials.
In addition, when the charge transport material is used in a mixture with the light emitting layer, the amount of the charge transport material used varies depending on the type of compound used, etc., but can be appropriately determined within a range that does not impair sufficient film forming properties and light emission characteristics. Good. Usually, it is preferably 1 to 40% by weight, more preferably 2 to 30% by weight, based on the light emitting material.
[0035]
Next, a typical method for manufacturing an organic EL element using the light emitting material of the present invention will be described. As the anode or cathode which is transparent or translucent, a transparent or translucent electrode formed on a transparent substrate such as glass or transparent plastic is used.
As the material for the anode, a conductive metal oxide film, a translucent metal thin film, or the like is used. Specifically, a film (NESA or the like) made of conductive glass made of indium / tin / oxide (ITO), tin oxide, or the like, a thin film of gold, platinum, silver, copper, or the like is used. As a manufacturing method, a vacuum deposition method, a sputtering method, a plating method, or the like is used.
[0036]
On the anode, the above-described polymeric fluorescent substance or a light-emitting layer containing the polymeric fluorescent substance and a charge transporting material is formed as a luminescent material. Examples of the forming method include spin coating methods, casting methods, dipping methods, bar coating methods, roll coating methods and the like using melts, solutions or mixed solutions of these materials. A method of forming a film by a coating method such as a spin coating method, a casting method, a dipping method, a bar coating method, or a roll coating method is particularly preferable.
[0037]
The film thickness of the light emitting layer is preferably 1 nm to 1 μm, more preferably 2 to 500 nm. In order to increase the current density and increase the light emission efficiency, the range of 5 to 200 nm is preferable.
In addition, when the light emitting layer is thinned by a coating method, in order to remove the solvent, it is preferably 30 to 300 ° C., more preferably 60 to 200 ° C. under reduced pressure or an inert atmosphere after forming the light emitting layer. It is desirable to heat and dry at a temperature.
[0038]
When a hole transport layer is laminated under the light emitting layer, it is preferable to form the hole transport layer before providing the light emitting layer by the above film forming method.
The method for forming the hole transport layer is not particularly limited, but includes a vacuum deposition method from a powder state, or a spin coating method after being dissolved in a solution, a casting method, a dipping method, a bar coating method, a roll coating method, etc. Use a coating method, or a coating method such as a spin coating method, casting method, dipping method, bar coating method, roll coating method, etc. after mixing and dispersing a polymer compound and a charge transport material in a solution state or a molten state. Can do.
The polymer compound to be mixed is not particularly limited, but those that do not extremely inhibit charge transport are preferable, and those that do not strongly absorb visible light are preferably used.
[0039]
For example, poly (N-vinylcarbazole), polyaniline and derivatives thereof, polythiophene and derivatives thereof, poly (p-phenylene vinylene) and derivatives thereof, poly (2,5-thienylene vinylene) and derivatives thereof, polycarbonate, polyacrylate, Examples include polymethyl acrylate, polymethyl methacrylate, polystyrene, polyvinyl chloride, and polysiloxane.
In terms of easy film formation, it is preferable to use a coating method when using a polymer compound.
[0040]
The thickness of the hole transport layer needs to be at least a thickness that does not cause pinholes. However, if the thickness is too large, the resistance of the device increases and a high driving voltage is required, which is not preferable. Therefore, the thickness of the charge transport layer is preferably 1 nm to 1 μm, more preferably 2 nm to 500 nm, and particularly preferably 5 to 200 nm.
[0041]
In addition, when an electron transport layer is further laminated on the light emitting layer, it is preferable to form the electron transport layer on the light emitting layer after the light emitting layer is provided by the film forming method described above.
[0042]
The method for forming the electron transport layer is not particularly limited, but it can be applied by vacuum deposition from a powder state, spin coating after dissolving in a solution, casting, dipping, bar coating, roll coating, or the like. Or a coating method such as a spin coating method, a casting method, a dipping method, a bar coating method, or a roll coating method after mixing and dispersing a polymer compound and a charge transport material in a solution state or a molten state. it can.
The polymer compound to be mixed is not particularly limited, but those that do not extremely inhibit charge transport are preferable, and those that do not strongly absorb visible light are preferably used.
[0043]
For example, poly (N-vinylcarbazole), polyaniline and derivatives thereof, polythiophene and derivatives thereof, poly (p-phenylene vinylene) and derivatives thereof, poly (2,5-thienylene vinylene) and derivatives thereof, polycarbonate, polyacrylate, Examples include polymethyl acrylate, polymethyl methacrylate, polystyrene, polyvinyl chloride, and polysiloxane.
In terms of easy film formation, it is preferable to use a coating method when using a polymer compound.
[0044]
The film thickness of the electron transport layer needs to be at least a thickness that does not cause pinholes. However, if the thickness is too large, the resistance of the device increases and a high driving voltage is required, which is not preferable. Therefore, the thickness of the electron transport layer is preferably 1 nm to 1 μm, more preferably 2 to 500 nm, and particularly preferably 5 to 200 nm.
[0045]
Next, the cathode described above is provided on the light emitting layer or the electron transport layer. As the method for producing the cathode, as described above, a vacuum deposition method, a sputtering method, or the like is used.
[0046]
[Action]
The organic EL device of the present invention is excellent because it uses a polymer material having a relatively high melting point and decomposition temperature, is thermally stable, and can easily form a light emitting layer by a coating method. This is because an organic EL element having high luminance and high luminous efficiency can be easily produced. Furthermore, by using a cathode made of an alloy containing 0.01 wt% or more and 10 wt% or less of an alkali metal, since the cathode has high electron injection efficiency, the light emitting efficiency of the device is high and the driving voltage is low. In addition, the durability of the cathode is increased by the action of the second and third metal layers, so that the lifetime can be extended, and it is considered that there is an effect of suppressing the generation of dark spots.
[0047]
【Example】
Examples of the present invention are shown below, but the present invention is not limited to these.
Here, for the number average molecular weight, the number average molecular weight in terms of polystyrene was determined by gel permeation chromatography (GPC) using chloroform as a solvent.
Example 1
<Synthesis of polymeric fluorescent substance 1>
2,5-Dioctyloxy-p-xylylene dibromide was reacted with triphenylphosphine in N, N-dimethylformamide solvent to synthesize phosphonium salts. 47.8 parts by weight of the obtained phosphonium salt and 6.7 parts by weight of terephthalaldehyde were dissolved in ethyl alcohol. An ethyl alcohol solution containing 5.8 parts by weight of lithium ethoxide was dropped into an ethyl alcohol solution of a phosphonium salt and a dialdehyde and polymerized at room temperature for 3 hours. After standing overnight at room temperature, the precipitate was filtered off, washed with ethyl alcohol, dissolved in chloroform, and ethanol was added to form a precipitate again. The obtained precipitate was dried under reduced pressure to obtain 8.0 parts by weight of a polymer. This is called polymeric fluorescent substance 1.
The repeating unit of the polymeric fluorescent substance 1 calculated from the monomer charge ratio and the molar ratio thereof are shown below.
[Formula 4]

The number average molecular weight in terms of polystyrene of the polymeric fluorescent substance 1 is 1.0 × 10 ^Four Met. The structure of the polymeric fluorescent substance 1 was confirmed by infrared absorption spectrum and NMR.
[0048]
<Creation and evaluation of device>
A glass substrate with an ITO film having a thickness of 40 nm was formed by sputtering using a 1.0 wt% chloroform solution of polyvinyl carbazole to a thickness of 50 nm by dipping. Further, a 1.0 wt% toluene solution of polymeric fluorescent substance 1 was used to form a film with a thickness of 50 nm by spin coating.
Furthermore, after drying this at 150 degreeC under pressure reduction for 1 hour, as an electron carrying layer, tris (8-quinolinol) aluminum (henceforth, Alq). _Three May be written. ) Was deposited to a thickness of 35 nm at a rate of 0.1 to 0.2 nm / s. A lithium-aluminum alloy (lithium concentration: 1 wt%) was deposited as a first metal layer on the cathode to a thickness of 40 nm to produce an organic EL device. The degree of vacuum during deposition is 8 × 10 ^-6 It was below Torr.
When a voltage of 12.5 V was applied to this element, the current density was 32.1 mA / cm. ² Current flows and the brightness is 1892 cd / m ² Yellow-green EL emission was observed. The luminous efficiency at this time was 5.9 cd / A. The brightness was almost proportional to the current density. Further, the EL peak wavelength was 540 nm, which substantially coincided with the fluorescence peak wavelength of the thin film of polymeric fluorescent substance 1, and EL emission from polymeric fluorescent substance 1 was confirmed.
This element has an initial luminance of 200 cd / m. ² When constant current driving was performed, the occurrence of dark spots was small, and the time until the luminance was reduced to half was 310 hours or more.
[0049]
Comparative Example 1
A device was prepared in the same manner as in Example 1 except that a magnesium-silver alloy (weight ratio Mg: Ag = 9: 1) having a thickness of 50 nm was used instead of the lithium-aluminum alloy as the first metal layer of the cathode. did. When a voltage of 12.5 V was applied to this element, the current density was 44.5 mA / cm. ² Current flows and the brightness is 1445 cd / m ² Yellow-green EL emission was observed. The luminous efficiency at this time was 3.3 cd / A. The brightness was almost proportional to the current density. Further, the EL peak wavelength was 540 nm, which substantially coincided with the fluorescence peak wavelength of the thin film of polymeric fluorescent substance 1, and EL emission from polymeric fluorescent substance 1 was confirmed.
This element has an initial luminance of 200 cd / m. ² When the device was driven at a constant current, dark spots were generated more than in the device of Example 1, and the luminance was reduced by half in about 250 hours.
[0050]
Comparative Example 2
A device was prepared in the same manner as in Example 1 except that aluminum having a thickness of 50 nm was used instead of the lithium-aluminum alloy as the first cathode layer. When a voltage of 12.5 V was applied to this element, the current density was 1.14 mA / cm. ² Current flows and the luminance is 21 cd / m ² Yellow-green EL emission was observed. The luminous efficiency at this time was 1.8 cd / A. The brightness was almost proportional to the current density. Further, the EL peak wavelength was 536 nm, which substantially coincided with the fluorescence peak wavelength of the thin film of the polymeric fluorescent substance 1, and EL emission from the polymeric fluorescent substance 1 was confirmed.
This element has an initial luminance of 20 cd / m. ² When constant current driving was performed, dark spots were generated more than in the device of Example 1, and the luminance was reduced by half in about 30 hours.
[0051]
[Table 1]

Thus, the organic EL device using the layer made of the polymeric fluorescent substance of Example 1 and the alkali metal alloy layer for the cathode is the organic of Comparative Examples 1 and 2 in which the alkali metal alloy layer is not used for the cathode. Excellent EL characteristics such as higher luminance and higher luminous efficiency than EL elements were exhibited.
[0052]
Example 2
Example 1 except that after the lithium-aluminum alloy was vapor-deposited as the first metal layer of the cathode, gold was deposited to 10 nm as the second metal layer, and then 500 nm of indium was vapor-deposited as the third metal layer. A device was prepared by the same method.
When this device was stored in air for 3 days and then driven at a direct current of 10 V, bright light emission without dark spots was obtained.
[0053]
Comparative Example 3
When the device in which the devices of Comparative Examples 1 and 2 were prepared was stored in the air for 3 days and then was driven at a direct current of 10 V, more dark spots were generated than in the device of Example 2, and about 80% of the region emitted light. I did not.
Thus, an alkali metal alloy layer is formed on the layer made of the polymeric fluorescent substance of Example 2 and the first metal layer of the cathode, gold is used as the second metal layer, and then indium is used as the third metal layer. The organic EL device used as the EL device exhibited superior EL characteristics such as suppressing the occurrence of dark spots as compared with the organic EL devices of Comparative Examples 1 and 2 using a magnesium silver alloy or aluminum as the cathode.
[0054]
【The invention's effect】
The organic EL device of the present invention has high brightness, high luminous efficiency, low driving voltage, is easy to produce, and hardly generates dark spots. Therefore, a device such as a planar light source or a flat panel display as a backlight. Can be preferably used.

Claims (9)

In an organic electroluminescence device having at least a light emitting layer between a pair of anodes and cathodes, at least one of which is transparent or translucent, the light emitting layer has fluorescence in a solid state, and is represented by the following general formula (1) A metal phosphor having a repeating unit represented by 50 mol% or more of all repeating units and having a polystyrene-equivalent number average molecular weight of 10 ³ to 10 ⁷ , and the cathode is one or more layers of metal A metal layer adjacent to the light emitting layer (referred to as a first metal layer) having a thickness of 10 to 300 nm, the first metal layer being an alkali metal, and stabilizing the first metal allowed to second mixing a metal layer or an alloy layer made of a metal, said second metal is selected silver, zinc, aluminum and indium, said first metal of said mixed metal or alloy The organic electroluminescent device degree is characterized by a 1 to 2 wt%.

(Here, Ar is an arylene group or heterocyclic compound group having 4 to 20 carbon atoms involved in the conjugated bond, R and R ′ are each independently hydrogen, an alkyl group having 1 to 20 carbon atoms. And a group selected from the group consisting of an aryl group having 6 to 20 carbon atoms, a heterocyclic compound having 4 to 20 carbon atoms, and a cyano group.) Adjacent to the first metal layer, a second metal layer made of a metal selected from the group consisting of gold, silver, platinum, aluminum, titanium, niobium, tantalum, chromium, iron, cobalt and nickel is laminated. The organic electroluminescence device according to claim 1, wherein the thickness of the second metal layer is 1-1000 nm. 2. The electroluminescent device according to claim 1, wherein a metal layer having a Young's modulus of 1 to 60 GPa and adjacent to the first metal layer is different from the first metal layer . 2. The electroluminescent device according to claim 1, wherein a metal layer made of indium, an indium magnesium alloy, lead, bismuth or antimony is further laminated adjacent to the first metal layer. 3. The electroluminescent device according to claim 2, wherein a third metal layer made of a metal having a Young's modulus of 1 to 60 GPa is further laminated adjacent to the second metal layer. The organic electroluminescent device according to any one of claims 1 to 5, characterized in that the alkali metal is selected from lithium, potassium or rubidium. Between the cathode and the light emitting layer, the organic electroluminescent device according to claim 1, adjacent to the light emitting layer, characterized in that a layer formed of an electron transporting material. 8. The organic electroluminescence device according to claim 1 , wherein a layer made of a hole transport material is provided adjacent to the light emitting layer between the anode and the light emitting layer. A layer made of an electron transporting material is provided adjacent to the light emitting layer between the cathode and the light emitting layer, and a layer made of a hole transporting material is adjacent to the light emitting layer between the anode and the light emitting layer. The organic electroluminescent element according to claim 1, wherein the organic electroluminescent element is provided.